This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to Patent Application No. 0001554-5 filed in Sweden on Apr. 28, 2000; the entire content of which is hereby incorporated by reference.
This invention relates to a milling tool of the type that comprises a body that is rotatable around a geometrical center and has an envelope surface in which is arranged at least one set of tangentially spaced-apart cutting members. Each cutting member features a cutting edge, the ends of which are spaced apart along the axis.
In such types of previously known milling tools for metalworking, all cutting members have one and the same clearance angle, which is generally within the range of 7-15xc2x0 and frequently amounts to 10-11xc2x0. During practical milling, the ability of the tool to remove metal is often limited by the stability of the system (i.e., the cutting members, workpiece, machine tool). When milling with cutting members in the form of indexible inserts, the stability, and thereby also the ability of the milling tool to remove metal, can be improved by geometrical optimization of the rake and flank surfaces of the cutting members, i.e. by choosing optimal cutting angles. During the milling of shoulders in a workpiece, for instance, milling at angles in relation to the end face of the milling tool, in the range of 30-95xc2x0, it is necessary that the axial, radial and cutting edge angles of the cutting members be adapted to the angle which the shoulder is to have; also, the line of the cutting edge is shaped to match the shape of the shoulder which is to be generated. The optimization of the geometry of the rake and clearance angles of the cutting members in order to gain stability, and thus improved metal-removing capacity leads, however, to the fact that only one single milling tool diameter can generate the desired angle of the shoulder. In other words, the individual milling tool can only be designed with one single diameter for each purpose, in order to satisfy both the requirement for a predetermined angle of the shoulder as well as the requirement for an optimized rake and clearance geometry from a stability point of view. It should also be pointed out that, in practice, unstable milling tools give a mediocre machining precision with respect to the flatness (smoothness) of the machined surface. An unstable, vibrating milling tool thus gives rise to at least small wavy formations on the machined surface of the workpiece.
The present invention aims at obviating the above-mentioned inconveniences of previously known milling tools and at providing an improved milling tool. Thus, a primary aim of the invention is to provide a milling tool which is capable of working in a stable, substantially vibration free way, and at the same time generate machined surfaces having a high degree of flatness. It is also an aim to provide a milling tool which at a given diameter can be used for machining, for instance, different types of shoulders while at the same time maintaining good machining precision as well as a stable operation.
According to the invention, a rotatable milling tool comprises a body, and at least one set of circumferentially spaced cutting members. The body defines a longitudinal axis and includes an envelope surface. The set of cutting members includes at least three cutting members mounted in the envelope surface. Each cutting member includes a flank surface and a cutting edge disposed adjacent to the flank surface. Each cutting edge has axially spaced apart ends. The flank surface of each cutting member forms a clearance angle with a tangent extending through the respective cutting edge. One of the flank surfaces has a larger clearance angle than at least two flank surfaces in the same set.